Certain applications require high resolution angular sensor systems. For example, a high resolution angular sensor system with respect to time sampling and angular resolution is used to implement a high-quality, directly-driven steering actuator in a steer-by-wire system of a vehicle. The steering actuator is at the upper end of the steering column in the vicinity of the driver. Such an angular sensor system is required in order that the actuator controller be able to measure the finest angular changes and thus the smallest changes in torque. Stringent control quality requirements exclude an angular sensor system having hysteresis in the range of the angular resolution. Thus, using an angular sensor system based on purely gear driven measurement technology is problematic.
For a steer-by-wire system in which no permanent connection exists between the steering wheel/steering actuator and the steering kinematic mechanism, and thus no over rotation protection is present for the conventional connection of the electrical components in the steering wheel with the spiral cassette used in the vehicle, it is necessary to cover an absolute measurement region that includes a plurality of revolutions of the actuator.
DE 101 10 785 C2 describes a steering angle sensor. The angle sensor includes a counter wheel that is driven by a shaft having a magnetic encoding system. Magnetic field sensors detect this encoding. The number of revolutions of the counter wheel, and thereby the shaft, can be determined from the sine and cosine shaped output signals of the sensors. Additionally, the shaft directly drives an encoding disk. A scanner detects the encoding of the encoding disk from which the angular position of the encoding disk can be determined within a single revolution. The absolute rotational angle of the angle sensor can be obtained from the collective evaluation of the sensor information from the counter wheel and the encoding disk. The precision that can be achieved for angle detection thus significantly depends on the encoding system applied on the encoding disk.